HARPS spectropolarimetry of Herbig Ae/Be stars

Our knowledge of the presence and the strength of magnetic fields in intermediate‐mass pre‐main‐sequence stars remains very poor. We present new magnetic field measurements in six Herbig Ae/Be stars observed with HARPS in spectropolarimetric mode. We downloaded from the European Southern Observatory (ESO) archive the publically available HARPS spectra for six Herbig Ae/Be stars. Wavelength shifts between right‐ and left‐hand side circularly polarised spectra were interpreted in terms of a longitudinal magnetic field 〈B_z〉, using the moment technique introduced by Mathys. The application of the moment technique to the HARPS spectra allowed us in addition to study the presence of the crossover effect and quadratic magnetic fields. Our search for longitudinal magnetic fields resulted in first detections of weak magnetic fields in the Herbig Ae/Be stars HD 58647 and HD 98922. Further, we confirm the previous tentative detection of a weak magnetic field in HD 104237 by Donati et al. and confirm the previous detection of a magnetic field in the Herbig Ae star HD 190073. Surprisingly, the measured longitudinal magnetic field of HD 190073, 〈B_z〉 = 91 ± 18 G at a significance level of 5σ is not in agreement with the measurement results of Alecian et al. (2013), 〈B_z〉 = –10 ± 20 G, who applied the LSD method to exactly the same data. No crossover effect was detected for any star in the sample. Only for HD 98922 the crossover effect was found tobe close to 3σ with a measured value of –4228 ± 1443 km s^–1 G. A quadratic magnetic field of the order of 10 kG was detected in HD 98922, and of ∼3.5 kG in HD 104237. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Evolution of magnetic fields in stars across the upper main sequence: II. Observed distribution of the magnetic field geometry

We re‐discuss the evolutionary state of upper main sequence magnetic stars using a sample of Ap and Bp stars with accurate Hipparcos parallaxes and definitely determined longitudinal magnetic fields. We confirm our previous results obtained from the study of Ap and Bp stars with accurate measurements of the mean magnetic field modulus and mean quadratic magnetic fields that magnetic stars of mass M < 3 M_⊙ are concentrated towards the centre of the main‐sequence band. In contrast, stars with masses M > 3 M_⊙ seem to be concentrated closer to the ZAMS. The study of a few known members of nearby open clusters with accurate Hipparcos parallaxes confirms these conclusions. Stronger magnetic fields tend to be found in hotter, younger and more massive stars, as well as in stars with shorter rotation periods. The longest rotation periods are found only in stars which spent already more than 40% of their main sequence life, in the mass domain between 1.8 and 3 M_⊙ and with log g values ranging from 3.80 to 4.13. No evidence is found for any loss of angular momentum during the main‐sequence life. The magnetic flux remains constant over the stellar life time on the main sequence. An excess of stars with large obliquities β is detected in both higher and lower mass stars. It is quite possible that the angle β becomes close to 0. in slower rotating stars of mass M > 3 M_⊙ too, analog to the behaviour of angles β in slowly rotating stars of M < 3 M_⊙. The obliquity angle distribution as inferred from the distribution of r ‐values appears random at the time magnetic stars become observable on the H‐R diagram. After quite a short time spent on the main sequence, the obliquity angle β tends to reach values close to either 90. or 0. for M < 3 M_⊙. The evolution of the obliquity angle β seems to be somewhat different for low and high mass stars. While we find a strong hint for an increase of β with the elapsed time on the main sequence for stars with M > 3 M_⊙, no similar trend is found for stars with M < 3 M_⊙. However, the predominance of high values of β at advanced ages in these stars is notable. As the physics governing the processes taking place in magnetised atmospheres remains poorly understood, magnetic field properties have to be considered in the framework of dynamo or fossil field theories. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Galactic distribution of WR stars

The recent VIIth Catalogue of Galactic Wolf-Rayet Stars lists 227 Population I WR stars, comprising 127 WN, 87 WC, 10 WN/WC and 3 WO stars. Additional discoveries bring the census to 234 WR stars. A re-determination of the optical photometric distances and the galactic distribution of WR stars shows in the solar neighbourhood a projected surface density of 2.7 WR stars per kpc², a N _WC/N _WN number ratio of 1.3, and a WR binary frequency of 40 %.The galactocentric distance (R _WR) distribution per subtype showsR _WN and R _WC decreasing with WN and WC subtypes. This revised version was published online in September 2006 with corrections to the Cover Date.     

Starspots

Starspots are created by local magnetic fields on the surfaces of stars, just as sunspots. Their fields are strong enough to suppress the overturning convective motion and thus block or redirect the flow of energy from the stellar interior outwards to the surface and consequently appear as locally cool and therefore dark regions against an otherwise bright photosphere (Biermann in Astronomische Nachrichten 264:361, 1938; Z Astrophysik 25:135, 1948). As such, starspots are observable tracers of the yet unknown internal dynamo activity and allow a glimpse into the complex internal stellar magnetic field structure. Starspots also enable the precise measurement of stellar rotation which is among the key ingredients for the expected internal magnetic topology. But whether starspots are just blown-up sunspot analogs, we do not know yet. This article is an attempt to review our current knowledge of starspots. A comparison of a white-light image of the Sun (G2V, 5 Gyr) with a Doppler image of a young solar-like star (EK Draconis; G1.5V, age 100 Myr, rotation 10 × Ω _Sun) and with a mean-field dynamo simulation suggests that starspots can be of significantly different appearance and cannot be explained with a scaling of the solar model, even for a star of same mass and effective temperature. Starspots, their surface location and migration pattern, and their link with the stellar dynamo and its internal energy transport, may have far reaching impact also for our understanding of low-mass stellar evolution and formation. Emphasis is given in this review to their importance as activity tracers in particular in the light of more and more precise exoplanet detections around solar-like, and therefore likely spotted, host stars.     

High-luminosity single carbon stars in stellar and galactic evolution

Summary In the solar neighborhood, approximately half of all intermediate mass main sequence stars with initially between 1 and about 5 Mbecome carbon stars with luminosities near 10⁴ L for typically less than 10⁶ years. These high luminosity carbon stars lose mass at rates nearly always in excess of 10^–7 M yr^–1 and sometimes in excess of 10^–5 M yr^–1. Locally, close to half of the mass returned into the interstellar medium by intermediate mass stars before they become white dwarfs is during the carbon star phase. A much greater fraction of lower metallicity stars become carbon-rich before they evolve into planetary nebulae than do higher metallicity stars; therefore, carbon stars are much more importan t in the outer than in the inner Galaxy.     

Magnetic,chemically peculiar (CP2) stars in the SuperWASP survey

The magnetic chemically peculiar (CP2) stars of the upper main sequence are well‐suited for investigating the impact of magnetic fields on the surface layers of stars, which leads to abundance inhomogeneities (spots) resulting in photometric variability. The light changes are explained in terms of the oblique rotator model; the derived photometric periods thus correlate with the rotational periods of the stars. CP2 stars exhibiting this kind of variability are classified as α² Canum Venaticorum (ACV) variables. We have analysed around 3850000 individual photometric WASP measurements of magnetic chemically peculiar (CP2) stars and candidates selected from the catalogue of Ap, HgMn, and Am stars, with the ultimate goal of detecting new ACV variables. In total, we found 80 variables, from which 74 are reported here for the first time. The data allowed us to establish variability for 23 stars which had been reported as probably constant in the literature before. Light curve parameters were obtained for all stars by a least‐squares fit with the fundamental sine wave and its first harmonic. Because of the scarcity of Strömgren uvbyβ measurements and the lack of parallax measurements with an accuracy better than 20%, we are not able to give reliable astro‐physical parameters for the investigated objects. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

New magnetic field measurements of β Cephei stars and slowly pulsating B stars

We present the results of the continuation of our magnetic survey with FORS 1 at the VLT of a sample of B‐type stars consisting of confirmed or candidate β Cephei stars and Slowly Pulsating B (hereafter SPB) stars, along with a small number of normal B‐type stars. A weak mean longitudinal magnetic field of the order of a few hundred Gauss was detected in three β Cephei stars and two stars suspected to be β Cephei stars, in five SPB stars and eight stars suspected to be SPB stars. Additionally, a longitudinal magnetic field at a level larger than 3σ has been diagnosed in two normal B‐type stars, the nitrogen‐rich early B‐type star HD 52089 and in the B5 IV star HD 153716. Roughly one third of β Cephei stars have detected magnetic fields: Out of 13 β Cephei stars studied to date with FORS 1, four stars possess weak magnetic fields, and out of the sample of six suspected β Cephei stars two show a weak magnetic field. The fraction of magnetic SPBs and candidate SPBs is found to be higher: Roughly half of the 34 SPB stars have been found to be magnetic and among the 16 candidate SPBs eight stars possess magnetic fields. In an attempt to understand why only a fraction of pulsating stars exhibit magnetic fields, we studied the position of magnetic and non‐magnetic pulsating stars in the H‐R diagram. We find that their domains in the H‐R diagram largely overlap, and no clear picture emerges as to the possible evolution of the magnetic field across the main sequence. It is possible that stronger fields tend to be found in stars with lower pulsating frequencies and smaller pulsating amplitudes. A somewhat similar trend is found if we consider a correlation between the field strength and the v sin i ‐values, i.e. stronger magnetic fields tend to be found in more slowly rotating stars (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Red supergiants in the LMC – III: luminous F and G stars

New BVRI observations for 40 and spectrophotometric measurements for 3 F to G LMC supergiant candidates (and 3 galactic F to G supergiants) are presented. The errors of the BVRI data are 0.01 to 0.03 mag in most cases. The wavelength range of the spectra is 3400 to 6400 Å, their resolution 10 Å. The mean error of the fluxes is 0.03 mag. Spectral indices measuring the strengths of the Hβ, Hγ, Hδ, NaD and CaII H+K lines, the CHα₀ and CNβ₀ bands, of the Balmer jump and the slope of the continuum redwards are discussed as measures of effective temperature and luminosity on the basis of galactic stars with accurate MK types and parallaxes. The Hγ line and the continuum gradient are very good temperature criteria, the CHα₀ band and especially the Balmer jump for luminosity. The luminosity classification given for F to G supergiant candidates in the LMC in the literature is often doubtful. 5 of the 3 stars observed spectrophotometrically turn out to be probably galactic foreground dwarfs on the basis both of the Balmer jump and the comparison of their flux distributions with synthetic ones based on the Kurucz model atmospheres. Surface gravities derived purely on the basis of flux distributions and such ones given by models of stellar evolution agree with each other for dwarfs and giants only. For supergiants the former are about 1.0 dex higher than the latter. As a consequence effective temperatures and metallicities given by these two methods deviate from each other for such stars, too. The intrinsic colours and temperatures of galactic and LMC supergiants do not differ. With absolute magnitudes up to -9.6 mag the upper luminosity limit in the LMC does not exceed that in the Galaxy, where Ia-0 supergiants have M_V of up to -9.5 mag. The metallicities of the supergiants show a rather large scatter. Nevertheless the mean metallicities of 0.0 ± 0.09 dex for the Galaxy and -0.6 ± 0.10 dex for the LMC agree well with other observations.     

The winds of WC10 central stars of planetary nebulae

We present the results of an analysis of the winds of two WC10 central stars of planetary nebulae, CPD-56°8032 and He 2-113. These two stars have remarkably similar spectra, although the former exhibits somewhat broader emission line widths. High resolution spectra (up to R=50 000) were obtained in May 1993 for both objects at the 3.9 m AAT, using the UCL Echelle Spectrograph. The fluxes in individual Cii auto-ionising multiplet components, many of which were blended, were derived. Lines originating from auto-ionising resonance states situated in the C²⁺ continuum are very sensitive to the electron temperature, since the population of the these levels is close to LTE. The measured widths and profile shapes of these transitions are presented and are in excellent agreement with those predicted on the basis of their calculated auto-ionising lifetimes. The wind electron temperature is derived for both stars from the ratio of the fluxes in four such transitions (T _e =18 500 K±1 500 K for CPD-56° 8032 andT _e =13 600 K±800 K for He 2-113). Optical depth effects are investigated using normal recombination lines to obtain an independent wind electron temperature estimate in excellent agreement with the dielectronic line analysis.     

Photometric observations and orbital period variations of HS 0705 + 6700 and NY Vir

We present photometric observations of two post-common-envelope stars, NY Vir (=PG 1336-018) and HS 0705 + 6700. The V band CCD observation of NY Vir was performed by a 40 cm telescope at Ege University Observatory and the R band observations of HS 0705 + 6700 were performed by 100 cm telescope at TÜB?TAK National Observatory. The new light curves were analyzed by the WD code and the physical parameters of stars were determined. We obtained new mid-eclipse timings for HS 0705 + 6700 and combined them with those previously published data. The analysis of the O-C residuals yields a period of about 8.06 ± 0.28 yr and an amplitude of 98.5 s for the system HS 0705 + 6700, which is attributed to the third star physically bounded to the evolved eclipsing pair. A mass function of 1.2 × 10⁻⁴ M_⊙ for the third star is obtained. The existence of a third star is also confirmed by the light curve analysis, indicating light contribution of about 0.043 at phase 0.25 in R-bandpass of the eclipsing pair. Using mass-luminosity relationship of the low mass stars we estimate a mass of 0.12 M_⊙ with an orbital inclination of about 20°. The O-C residuals obtained for the system NY Vir were represented by a downward parabola which indicates orbital period decrease in the system. Using the coefficient of quadratic term we calculate a rate of orbital period decrease of about dP/dt = −4.09 × 10⁻⁸days yr⁻¹. The period decrease we have measured in NY Vir may be explained by angular momentum loss from the binary system.     

X-ray Observations of Eight Young Open Star Clusters: I. Membership and X-ray Luminosity

We present a detailed investigation of X-ray source contents of eight young open clusters with ages between 4 to 46 Myr using archival X-ray data from XMM-Newton. The probable cluster memberships of the X-ray sources have been established on the basis of multi-wavelength archival data, and samples of 152 pre-main sequence (PMS) low mass (<2M _⊙), 36 intermediate mass (2–10M _⊙) and 16 massive (>10M _⊙) stars have been generated. X-ray spectral analyses of high mass stars reveal the presence of high temperature plasma with temperature <2 keV, and mean L _X/L _bol of 10^???6.9. In the case of PMS low mass stars, the plasma temperatures have been found to be in the range of 0.2 keV to 3 keV with a median value of ~1.3 keV, with no significant difference in plasma temperatures during their evolution from 4 to 46 Myr. The X-ray luminosity distributions of the PMS low mass stars have been found to be similar in the young star clusters under study. This may suggest a nearly uniform X-ray activity in the PMS low mass stars of ages ~4–14 Myr. These observed values of L _X/L _bol are found to have a mean value of 10^??3.6±0.4, which is below the X-ray saturation level. The L _X/L _bol values for the PMS low mass stars are well correlated with their bolometric luminosities, that implies its dependence on the internal structure of the low mass stars. The difference between the X-ray luminosity distributions of the intermediate mass stars and the PMS low mass stars has not been found to be statistically significant. Their L _X/L _bol values, however have been found to be significantly different from each other with a confidence level greater than 99.999% and the strength of X-ray activity in the intermediate mass stars is found to be lower compared to the low mass stars. However, the possibility of X-ray emission from the intermediate mass stars due to a low mass star in close proximity of the intermediate mass star can not be ruled out.     

On the behavior of the C 4267.261, 6578.052 and 6582.882 Å lines in chemically peculiar and standard stars

With the aim of investigating the possible particular behavior of carbon in a sample of chemically peculiar stars of the main sequence without turning to modeling, we performed spectroscopic observations of three important and usually prominent single ionized carbon lines: 4267.261, 6578.052 and 6582.882 Å. In addition, we observed a large number of standard stars in order to define a kind of normality strip, useful for comparing the observed trend for the peculiar stars. We paid particular attention to the problem of the determination of fundamental atmospheric parameters, especially for the chemically peculiar stars for which the abundance anomalies change the flux distribution in such a way that the classical photometric methods to infer effective temperatures and gravities parameter cannot be applied. Regarding CP stars, we found a normal carbon abundance in Hg–Mn, Si (with some exceptions) and He strong stars. He weak stars are normal too, but with a large spread out of the data around the mean value. A more complicated behavior has been noted in the group of SrCrEu stars: four out of seven show a strong overabundance, being the others normal.     

Gamma-ray burst energy spectra: theoretical models,old and new

The M, S and C stars may be placed in an evolutionary sequence on the basis of direct observation of the spectroscopic transitions on the AGB of rich intermediate-age clusters in the Magellanic Clouds, but some S and C stars cannot be accounted for in this way. The S stars in Centauri owe their peculiarity to a primordial enrichment in s-process elements. The J-type (¹³C-rich) carbon stars originate in a different way to the ordinary cool N-type carbon stars. Some of them have silicate-rich circumstellar dust, contrary to expectation. Some of the carbon-rich RV Tauri stars also have silicate-rich dust and in both cases it may be organised in a disc. Observational evidence for gas and dust ejection by ordinary N-type carbon stars has been found and may be inferred for some RV Tauri stars.     

The evolution of hydrogen-helium stars

According to the work of Truran and Cameron, and of others, on the chemical evolution of the Galaxy, the first generation of stars in the Galaxy contained principally massive objects. If big-bang nucleosynthesis was responsible for the formation of helium, the first generation of stars would contain about 80% hydrogen and 20% helium, to be consistent with the approximately 22% helium found in recent stellar evolutionary studies of the Sun. The present investigation has followed the pre-main sequence evolution and the main sequence evolution of stars of 5, 10, 20, 30, 100, and 200M . Normal stars in this entire mass range normally convert hydrogen into helium by the CN-cycle on the main sequence. the present hydrogen-helium stars of 5 and 10M must reach higher central temperatures in order to convert hydrogen to helium by the proton-proton chains. Consequently, the mean densities in the stars are greater, and the surface temperatures are higher than in normal stars. In the stars of 20M and larger, the proton-proton chains do not succed in supplying the necessary luminosity of the stars by the time the contraction has produced a central temperature near 10⁸K. At that point triple-alpha reactions generate small amounts of C¹², which then acts as a catalyst in the CN-cycle, the rate of which is then limited by the beta-decays occurring within the cycle. During the evolution of these more massive stars, the central temperature remains in the vicinity of 10⁸ K, and the surface temperature on the main sequence approaches 10⁵ K. The star of 200M becomes unstable against surface mass loss through radiation pressure in the later stages of its main sequence evolution, and these mass loss effects were not followed. Young galaxies containing these massive stars will have a very high luminosity, but if they have formed at one-tenth the present age of the universe or later, then the light from them will mainly reside in the visible or ultraviolet, rather than in the infrared as has been suggested by Partridge and Peebles.     

Evolution of Population II stars

The current knowledge of the evolution of Population II stars, as observed in galactic halos and globular clusters, is outlined. The recent theoretical results provided by an improved physical understanding of the stars are reported, with a particular emphasis upon those stellar evolutionary phases which are the keystones of the interpretation of globular cluster stars. Within the up–to–date theoretical scenario, the luminosity of the turn–off stars and horizontal branch stars, which are of fundamental importance for distance and age determinations, turns out to be fainter and brighter, respectively, in comparison with previous theoretical computations. The predicted absolute magnitude of RR Lyrae stars is consistent with the bright values suggested from the long distance scale (Sandage 1993), but the slope of the relation between and metallicity ([Fe/H]) agrees with that suggested from the short distance scale (see, e.g., Carney et al. 1992, Clementini et al. 1995), at least with [Fe/H]-1.3. As to the globular cluster ages, the new computations provide younger ages ( 10 Gyr–13 Gyr), weakening the conflict with current cosmological estimates. The recent results derived from the fitting of HIPPARCOS parallaxes of field subdwarfs to the fiducial main sequence of globular clusters are consistent with the up–to–date theoretical models. However, the direct determinations of , which are based on the HIPPARCOS proper motions and trigonometric parallaxes of field RR Lyrae stars, give fainter absolute magnitudes than those obtained from the improved evolutionary models. This seems to suggest that the problem of the globular cluster distance and age is still open. Received 6 April 1998     

The stellar mass spectrum of the open cluster NGC 3293

We have obtained and analyzed UBVRI CCD frames of the young, 4–10 Myr, open cluster NGC 3293 and the surrounding field in order to study its stellar content and determine the cluster’s IMF. We found significantly fewer lower mass stars, M≤2.5M _⊙, than expected. This is particularly so if a single age for the cluster of 4.6 Myr is adopted as derived from fitting evolutionary models to the upper main sequence. Some intermediate-mass stars near the main sequence in the HR diagram imply an age for the cluster of about 10 Myr. When compared with the Scalo (The stellar initial mass function. ASP conference series, vol. 24, p. 201, 1998) IMF scaled to the cluster IMF in the intermediate mass range, 2.5≤M/M _⊙≤8.0 where there is good agreement, the high mass stars have a distinctly flatter IMF, indicating an over abundance of these stars, and there is a sharp turnover in the distribution at lower masses. The radial density distribution of cluster stars in the massive and intermediate mass regimes indicate that these stars are more concentrated to the cluster core whereas the lower-mass stars show little concentration. We suggest that this is evidence supporting the formation of massive stars through accretion and/or coagulation processes in denser cluster cores at the expense of the lower mass proto-stars. R.W. Slawson and E.P. Horch are guest investigators at the University of Toronto Southern Observatory, Las Campanas, Chile.     

An updated period analysis for ER Orionis: A definitive solution

An updated period analysis for the overcontact eclipsing binary ER Orionis is presented. Featured is an improved derivation of parameters for the light time effect (LTE) due to the third star (in actuality, a pair of stars) utilising the latest set of eclipse timings. The very good fit between the eclipse timing differences (ETD) plot (otherwise known as an O–C diagram) and the theoretical ETD curve makes possible an improved determination of the rate of mass interchange between the binary pair, dm₁/dt = +1.83(6) × 10⁻⁷ M_ʘ/year. In addition, the mass of the companion system (in actuality, m₃ sin i) and the elements of its orbit were computed. A suggestion is made for a method of future determination of the inclination of the orbit of the companion system.     

Shocks and shells in hot star winds

Radiation-driven winds of hot, massive stars showvariability in UV and optical line profiles on time scales of hours to days.Shock heating of wind material is indicated by the observed X-ray emission. We present time-dependent hydrodynamical models of these winds, where flowstructures originate from a strong instability of the radiative driving. Recent calculations (Owocki 1992) of the unstable growth of perturbations were restricted by the assumptions of 1-D spherical symmetry and isothermality of the wind. We drop the latter assumption and include the energy transfer in the wind. This leads to a severe numerical shortcoming, whereby all radiative cooling zones collapse and the shocks become isothermal again. We propose a method to hinder this collapse. Calculations for dense supergiant winds then show: (1) The wind consists of a sequence of narrow and dense shells, which are enclosed by strong reverse shocks (with temperatures of 10⁶ to 10⁷ K) on their starward facing side. (2) Collisions of shells are frequent up to 6 to 7 stellar radii. (3) Radiative cooling is efficient only up to 4 to 6R _*. Beyond these radii, cooling zones behind shocks become broad and alter the wind structure drastically: all reverse shocks disappear, leaving regions ofpreviously heated gas.     

Masses and Radii of Low-Mass Stars: Theory Versus Observations

Eclipsing binaries with M-type components are still rare objects. Strong observational biases have made that today only a few eclipsing binaries with component masses below 0.6 M_⊙ and well-determined fundamental properties are known. However, even in these small numbers the detailed comparison of the observed masses and radii with theoretical predictions has revealed large disagreements. Current models seem to predict radii of stars in the 0.4--0.8 M_⊙ range to be some 5--15% smaller than observed. Given the high accuracy of the empirical measurements (a few percent in both mass and radius), these differences are highly significant. I review all the observational evidence on the properties of M-type stars and discuss a possible scenario based on stellar activity to explain the observed discrepancies.     

Studying young stellar populations in G345.5+1.5 molecular cloud

Using different sky surveys, we studied IRAS sources and embedded clusters located in the G345.5+1.5 region. Our analysis comprises multi-wavelength (optical to radio) data, exploited using various methods: photometry, near-infrared spectroscopy for ten stars in the embedded cluster DBS-114, and astrometry. We estimated the main parameters of the embedded stellar populations in the G345.5+1.5 molecular cloud, such as their extent, reddening, age, and mass. We also found a consistent distance value using different approaches. For each studied population, we classified several point objects as early main sequence stars, stars with infrared excess, and class I/II YSOs. For the particular case of DBS 114, our spectral classification revealed four B-type stars, and we used astrometric information from GAIA EDR3. The combination of optical and infrared information revealed an abnormal reddening law in some embedded clusters. Our analysis favored a scenario with a Lyman continuum emission excess at some of the studied stellar populations.